president obama will travel to boston on thursday to speak at an interfaith service. today, he vowed to find those responsible and labeled the bombings an act of terrorism. >> this was a heinous and cowardly act. and given what we now know about what took place, the fbi is investigating it as an act of terrorism. any time bombs are used to target innocent civilians, it is an act of terror. it will take time to follow every lead and determine what happened. but we will find out. we will find whoever harmed our citizens and we will bring them to justice. >> today we also are getting new video of the actual explosions. including the only tape we've seen taken by a woman actually running in the race. [ explosion ] . >> and new radio calls from first responders reveal the chaotic moments just after the explosions. >> we have reports of two explosions here. we have at least a dozen people with serious injuries. >> at least two explosions. a dozen serious injuries, a multiple injury incident. >> authorities are now asking anyone with potential photo or video evidence to come